Let's complete the sentences with the correct verb forms:

23. If he **gives** up smoking, as his doctor orders, he will soon be well again.

Explanation: This is a first conditional sentence. "Gives" is the present simple tense used in the if-clause, and "will be" is the future simple tense used in the main clause.

24. You would have to stay in bed if your health **did not improve**.

Explanation: This is a second conditional sentence. "Did not improve" is the simple past tense used in the if-clause, and "would have to stay" is the conditional form used in the main clause.

25. If I **had known** that you were ill, I **would have gone** to see you.

Explanation: This is a third conditional sentence. "Had known" is the past perfect tense used in the if-clause, and "would have gone" is the conditional perfect tense used in the main clause.

26. If she'd had enough money, she **would have bought** a car.

Explanation: This is a third conditional sentence. "Had had" is the past perfect tense used in the if-clause, and "would have bought" is the conditional perfect tense used in the main clause.

27. I **would buy** a car if you lend me some money.

Explanation: This is a second conditional sentence. "Would buy" is the conditional form used in the main clause, and "lend" is the base form of the verb used in the if-clause.

28. I **would have seen** him if I **had gone** to the party last night.

Explanation: This is a third conditional sentence. "Had gone" is the past perfect tense used in the if-clause, and "would have seen" is the conditional perfect tense used in the main clause.

29. We could have gone out if the weather **had not been** so bad.

Explanation: This is a third conditional sentence. "Had not been" is the past perfect tense used in the if-clause.

30. If the book **were not** so expensive, I **would buy** it.

Explanation: This is a second conditional sentence. "Were not" is the subjunctive mood used in the if-clause (indicating hypothetical or unreal situations), and "would buy" is the conditional form used in the main clause.

These corrections ensure that each sentence uses the appropriate verb tense or mood to convey the intended meaning accurately in English.